At 8,849 metres (29,032 ft), reaching the peak of Mount Everest has long been considered one of mountaineering’s greatest challenges.
However, climbers of the future might have an even tougher time as experts reveal that the world’s tallest mountain is growing by the day.
Researchers from University College London discovered that Mount Everest has already grown between 15 to 50m (49-164ft) in the past 89,000 years.
They claim this unexpected growth spurt is due to a nearby river eroding so much material that the mountain is getting lighter and springing upwards at a rate of 2mm per year.
Co-author Adam Smith says: ‘Mount Everest is a remarkable mountain of myth and legend and it’s still growing.’
Mount Everest is springing upwards at a rate of 2mm per year, researchers say. As erosion makes the mountain lighter, it is pushed upwards by the liquid mantle
At 8,848 meters (29,032ft) Mount Everest is the highest mountain in the world but researchers now say it is growing even taller by 2mm per year
Generally, the biggest peaks within a mountain range are all roughly the same size, perhaps only varying by a few hundred metres at the most.
Mr Smith told MailOnline: ‘Everest is 250m taller than K2, the world’s second highest peak, but K2 and the other peaks are only 50-100m taller than the subsequent highest peaks. In this sense, Everest is an anomaly.’
Not only is Everest unusually tall, but scientists now know that it is getting taller every year.
GPS instruments show that Everest’s peak pushes upwards at around 2mm per year.
But, until now, there hasn’t been a clear explanation as to why Everest is so much taller than its companions or how it continues to grow.
The answer, as the researchers write in Nature Geoscience, actually has nothing to do with Everest itself but comes down to the action of a nearby river.
Co-author Dr Jin-Gen Dai says: ‘An interesting river system exists in the Everest region – the upstream Arun River flows east at high altitude with a flat valley.
Researchers have found that erosion from rivers (illustrated in orange) around Everest, which is labelled here as Chomolungma using the Tibetan name, is causing the mountain to rise higher each year
89,000 years ago the gentle Arun River merged with the steep Kosi River (pictured), greatly increasing its erosive power and allowing it to remove billions of tonnes of rock and sediment from the area around Mount Everest
‘It then abruptly turns south as the Kosi river, dropping in elevation and becoming steeper.’
By studying the erosion rates of rivers in the region, Dr Dai and his colleagues found that these two rivers, the Arun and the Kosi, merged around 89,000 years ago.
When this happened, much more water was funnelled through the steep, narrow Kosi River – dramatically increasing its erosive power.
While it might not be obvious on the human timescale, over thousands of years this has led to the removal of billions of tonnes of rock and sediment from the area around Everest.
Slowly, this lightening process means that Everest literally floats upwards through a process called ‘isostatic rebound’.
Mount Everest (pictured) is around 250m (820ft) taller than the next tallest mountains. Researchers now think this could be due to the effects of the nearby river systems
As the Arun and the Kosi Rivers erode material from around the mountains, they become lighter and float higher on the liquid mantle beneath the Earth’s crust. This map shows how areas of high erosion (red) are near the mountains Everest (Chomolungma) and Makalu
Mr Smith explains: ‘The crust, the outermost layer of the Earth, “floats” on the mantle, which is a semi-liquid layer beneath the crust.
‘This is similar to how icebergs float on water.
‘The lighter, or less dense, a material is, the higher it floats in water, or on the mantle.’
Mr Smith says you can think about the area around Mt Everest like a pool float sitting on the surface of the water.
If you put weights onto the float, the force of gravity will be stronger than the force of the water pushing upwards and the float will sit lower in the water.
But, if you gradually take some of those weights away, you’ll notice that the float gradually rises up.
‘This has happened with Everest, as material close to Everest has been removed causing uplift or isostatic rebound,’ Mr Smith adds.
A process called isostatic rebound may explain why Everest is significantly taller than the other peaks in the Himalayan Mountain range (pictured)
This diagram shows the areas of highest (top) and lowest (bottom) elevation in the Himalayas. You can see that the highest points of Chomolungma (Everest) and Kanchenjunga are closest to the low point of the Kosi River
Over the 89,000 years since the Kosi and Arun rivers merged, they have removed enough weight to lift Everest somewhere between 49 and 164ft (15-50m), researchers say.
Since the material is being removed so close to Everest, the team believe this may be part of the reason that Everest is so much taller than peaks like K2.
But while the mountains are getting taller for now, this process will eventually hit its limit.
Mr Smith adds: ‘Everest cannot keep on growing forever.
‘I think the height of Everest is limited by the strength of rocks and amount of material or rock that we have available to make the mountain, which is finite.’
Everest isn’t the only mountain in the rage getting taller, however, as the isostatic uplift affects all nearby mountains.
The fastest-growing mountain in the range is Makalu, the fifth-highest mountain in the world at 8,485m (27,766ft), which has risen 60m (197ft) since the rivers merged.
However, Mr Smith does not believe the difference is great enough for Makalu to overtake Everest as the tallest peak in the world.
